The invention relates in general to barrier movement operators and in particular to a jack shaft garage door operator having a sensing apparatus for preventing cable associated with a pull-up cable drum from becoming slack during the operation of the door and for providing a positive door locking system.
One of the problems associated with jack shaft garage door operators is that while they are compact and may be conveniently used in garages which have little overhead room, they may present problems to the owners of the garage in that the cable may be payed out allowing the door to close under its own weight and if the door stalls or if the cable pay out drum rotates too far, the tension in the cable will drop and the cable may come off the drum necessitating a visit from a repairman. In addition, the jack shaft garage door operator does not provide any secure locking facility other than a lock at the bottom of the door, which may be tampered with by a burglar. If the door is not locked by some other means, the bottom lock may be forced or damaged and the door can be lifted open and the garage entered by an intruder.
U.S. Pat. No. 3,785,089 discloses a door operator having a winch member built into a tilting door and movable with it. A cable is attached to a wall member supporting the door and another end of the cable is connected to an extensible arm.
U.S. Pat. No. 2,185,828 discloses a catch for stopping a door from falling in the event that a sustaining cable or a counterbalance fails or breaks.
U.S. Pat. No. 4,385,471 discloses a door including a stopping member having a clip connection 29 which engages a cable. If the cable breaks, as shown in FIG. 4, the arm 27 rotates outwardly bringing a cam dog 26 having a plurality of teeth 32 into locking engagement with a roller 13a to prevent the roller 13a from moving, thereby suspending the door in position.
U.S. Pat. No. 4,520,591 to Calvagno discloses a system that is mechanically responsive to a break in a cable to prevent a door from falling.
French Patent No. 2634-815-A includes an xe2x80x9canti-dropxe2x80x9d safety mechanism having a cam plate 21 on either side of the door equipped with a convex toothed edge to engage a bracket in case of door suspension failure. None of the aforementioned documents teach or disclose solutions for preventing a door from being opened or from stopping an operation of a garage door operator to cause it to reverse to take up cable which may have inadvertently been payed off a cable drum of a jack shaft door operator.
What is needed is an improved barrier movement operator that avoids unwanted problems with the cable coming off the drum and provides security for the user.
A jack shaft garage door operator is useful for opening and closing a movable barrier such as a garage door. The jack shaft garage door operator embodying the present invention includes a drive unit having an electric motor therein for driving a torsion shaft sometimes called a jack shaft. The jack shaft is mounted above a door opening and usually has coupled to it a spring, or the like, for providing a restoring force to the jack shaft to help raise the door and to support a portion of the weight of the door that is not supported by the L-shaped rails that a door usually rides in. A pull-up cable drum is connected to the jack shaft to be rotated thereby and has a multi-strand steel pull-up cable connected thereto that may be payed out to lower a door or wound up to raise the door. The pull-up cable is typically connected to a bottom portion of the door and, when wound up, will cause the door to rise along vertical portions of L-shaped rails. A cable tension sensing apparatus is mounted on a wall having a door opening. The cable tension sensing apparatus includes cable guide to retain the cable a substantially fixed distance from the wall and a spring driven cable follower which urges against the cable extending between the drum periphery and the cable guide. An alerting switch is connected to the cable follower and sends a signal indicating loss of cable tension when the cable follower moves beyond a predetermined distance. Additionally, the movement of the cable follower moves a door blocking arrangement to a position to block movement of the door when being raised without use of the motor.
In the event that the cable is inadvertently payed out, for instance, by the door having reached the bottom of its travel and the operator continuing to run, the cable follower is allowed to move away from the wall by reduced tension (slack) in the cable and moves far enough that the alerting switch operates to generate a signal to which the operator responds by reversing the motor to raise the door. The garage door operator may otherwise be a conventional jack shaft garage door operator. The cable tension sensing apparatus prevents the cable from coming off the cable drum. In addition, a door stop for preventing the garage door from opening is attached to an upper panel of the garage door and, when in the closed position, is beneath the cable tension sensing apparatus when the door is pulled downwardly by full tension on the cable. When the cable follower moves as tension lessens in the cable, a sliding member is moved away from the wall above the door. If the door is attempted to be breached, for instance by an intruder attempting to lift the door, the cable becomes slack allowing the sliding member to come out from the wall so that it then engages compressionally a stop plate on the garage door thereby preventing further upward motion of the garage door.
It is an aspect of the present invention to provide a jack shaft garage door operator having a cable tension sensor for providing door operator actions reversal to prevent cable paying off a cable drum.
It is another aspect of the present invention to provide a jack shaft garage door operator having a door opening block adapted to engage a sliding member to prevent a door from being forced open.
Other advantages of the invention will become obvious to one of ordinary skill in the art upon a perusal of the following specification and claims in light of the accompanying drawings.